1. Field of the Invention
The present invention relates to a coordinates input apparatus which makes use of an elastic wave, particularly a plate elastic wave.
2. Related Background Art
A known coordinates input apparatus makes use of a CRT in combination with a light pen. The light pen is placed at a position on the CRT so that the position is sensed from the raster timing peculiar to the position. This known apparatus essentially requires a CRT and, hence, can be used only in high-class systems.
Another known coordinates input apparatus employs a tabular member on which is provided a specific electrode pattern. An electric current is made to flow through this electrode pattern and a voltage drop amount at an appointed position on the electrode pattern is measured, whereby the coordinates of the appointed position are determined. In this apparatus, however, the coordinates input apparatus cannot be made transparent because of the presence of the electrode pattern.
Both these known coordinates input apparatus are generally expensive and are not suitable for use in comparatively inexpensive products such as desk-top calculators and word processors.
Under these circumstances, a method has been proposed for detecting the coordinates by making use of vibration. More specifically, this method employs an input pen the end of which is vibrated and brought into cantact with a plate such a glass. The vibration applied to the plate is sensed by a sensor and the position of the pen is detected through measuring the vibration propagation time. In this case, the vibration is utilized in the form of surface wave which is liable to be disturbed by any flaw in the glass or by a touch by the user's finger, with the result that the accuracy of detection of coordinates is impaired.